1. Field of the Invention
The invention relates to improvements in a sandwich-wire antenna. More specifically, the invention relates to a sandwich-wire antenna which includes improved input transition means. The invention also relates to a sandwich-wire antenna which is disposed in a metallic channel having side walls, the side walls extending above the height of the radiating element of the antenna. 2. Description of Prior Art
The sandwich-wire antenna was first described by Rotman and Karas in IRE Convention Record, 1957, pp. 166-172 and in Microwave Journal, August 1959, pp. 29-33. In these publications, the sandwich-wire antenna was illustrated in the form of an undulating wire sandwiched between two straight wires. Hence the name of the antenna.
In this simplest form, the antenna radiates equally in two directions away from the plane of the wires and is therefore unsuitable for many applications where a single beam is required. Rotman and Karas recognize this in the same papers and therefore described several other implementations. In the most important of these, the two straight wires are replaced by an open rectangular metal channel or trough so that the antenna produces one beam which is directed substantially away from the channel. The undulating centre conductor may be formed from wire, or it may be printed as a flat metal track on a dielectric sheet. The height of the channel walls is normally chosen so that the edges are level with the centre conductor. This is a convenient arrangement for producing a planar array consisting of a number of sandwich-wire antennas. Several implementations of such an array have been built including the Doppler Navigation Antennas made by the applicant herein.
In cases when only a single linear antenna is required, the edges of the channel may be terminated with flanges or a horn flare to control the radiation pattern in the transverse plane.
Green and Whitrow IEEE Trans. AP-19, No. 5, September 1971, pp. 600-605, published a theoretical analysis of the sandwich-wire antenna in which they considered the possibility of extending the channel walls to a significant height above the plane of the centre conductor. This was done primarily for ease of mathematical modelling since part of their analysis treated the walls as extending to infinity although they also showed that certain choices of wall height are optimum in placing the aperture admittance of the channel in the correct phase relationship with the track radiation resistance so that wide-band operation may be obtained.
Hockham and Wolfson, Int. Symposium Antennas and Propagation, Seattle, 1979, pp. 645-648 and Second International conference on Antennas and Propagation, York University, 13th-16th April, 1981, (IEE) Part 1, pp. 11-14, described a sandwich-wire antenna which used thick walls projecting a small distance above the printed track. In this arrangement, the channel walls were in fact slotted waveguides, operating at a higher frequency band, so that the combination produced a dual-band antenna.
Shafai and Sebak, IEE Proceedings Vol. 132, Part H, No. 7, December 1985, pp. 433-439 have described a microstrip antenna, i.e., just using a printed dielectric sheet with a metal backing plate, but without any channels, where the use of the inverted track patterns on alternating tracks cancels cross-polarisation on the major axes of the antenna. However, in this arrangement, there will still be significant cross-polarisation away from the major axes, as the cancellation process does not operate completely in these areas.
Insofar as can be determined from the published literature, the methods of feeding sandwich-wire antennas have not been extensively investigated. In several cases, an antenna is fed by a simple coaxial connector at the input end. Another method, discussed by Graham and Dawson, 1st European Microwave Conference, London, September 1969, pp. 528-531, for a planar array of sandwich-wire antennas, is to project the centre conductors through the wall of a transverse waveguide to probe couple to the field in the waveguide.
Microstrip antennas are also known in the art as is illustrated in U.S. Pat. No. 4,197,545, Favaloro et al, Apr. 8, 1980, U.S. Pat. No. 4,369,447, Edney, Jan. 18, 1983, and U.S. Pat. No. 4,415,900, Kaloi, Nov. 15, 1983. However, none of these antennas are sandwich-wire-type antennas.